1. Field of the Invention
The present invention relates to a chuck for chucking a cutting tool such as a drill or end mill, and more particularly to a chuck in which a clamp sleeve is fitted onto the outer circumference of a chuck sleeve of a holder body via needle rollers, and in which, through rotation of the clamp sleeve in a clamping direction, the diameter of the chuck sleeve is reduced in order to tightly chuck a desired tool.
2. Description of the Related Art
A conventional chuck will be described with reference to FIG. 12. FIG. 12 is a cross-sectional view of a conventional tool chuck.
As shown in FIG. 12, the tool chuck has a holder body 1. The tool holder body 1 has a tapered shank portion 1A to be inserted into a spindle of an unillustrated machine tool, a gripping flange 1B formed at the larger-diameter end of the tapered shank portion 1A, and a chuck sleeve 1C that extends from the end surface of the flange 1B opposite the tapered shank portion 1A. The chuck sleeve 1C extends in the direction away from the tapered shank portion 1A such that the axis of the chuck sleeve 1C coincides with the axis of the tapered shank portion 1A. A tapered surface 1Ca is formed on the outer circumference of the chuck sleeve 1C such that the diameter of the surface 1Ca decreases toward the tip end thereof.
Reference numeral 2 denotes a roller-retaining sleeve which is fitted onto the outer circumference of the chuck sleeve 1C with a clearance therebetween. The diameter of the roller-retaining sleeve 2 decreases toward the tip end thereof substantially at the same rate as that of the tapered surface 1Ca of the chuck sleeve 1C. The roller-retaining sleeve 2 is held by a retainer ring 3 provided on the outer circumference of the tip end portion of the chuck sleeve 1C such that the roller-retaining sleeve 2 is prevented from coming off the chuck sleeve 1C.
In the roller-retaining sleeve 2, numerous needle rollers 4 are disposed to form a plurality of rows. The needle rollers are fitted into the roller-retaining sleeve 2 in such a manner that the needle rollers incline in the circumferential direction at a predetermined angle with respect to the center axis of the roller-retaining sleeve 2. Each of the needle rollers 4 has a diameter greater than the wall thickness of the roller-retaining sleeve 2, so that the portion of each needle roller 4 projecting inward from the inner circumferential surface of the roller retaining sleeve 2 is in contact with the tapered surface 1Ca of the chuck sleeve 1C, while the portion of each needle roller 4 projecting outward from the outer circumferential surface of the roller retaining-sleeve 2 is in contact with the inner circumferential surface of a clamp sleeve 5, which will be described below.
The clamp sleeve 5 is adapted to reduce the diameter of the chuck sleeve 1C to thereby tightly chuck a desired tool. The clamp sleeve 5 is fitted onto the outer circumference of the chuck sleeve 1C via the needle rollers 4 held by the roller-retaining sleeve 2. The clamp sleeve 5 has a tapered inner circumferential surface whose diameter decreases from the end facing the flange 1B toward the tip end thereof. Further, a sealing/retaining ring 6 is attached to the inner circumference of the bottom end portion of the clamp sleeve 5 adjacent to the flange 1B. The sealing/retaining ring 6 is in contact with the outer circumferential surface of the chuck sleeve 1C so as to provide a sealing function. The sealing/retaining ring 6 also abuts the end surface of the roller retaining sleeve 2 in order to prevent the clamp sleeve 5 from coming off the chuck sleeve 1C.
In the conventional chuck having the above-described structure, when a tool 7 is to be chucked, a spring collet 8 is fitted onto the shank 7A of the tool 7, and the shank 7A of the tool 7, together with the spring collet 8, is inserted into the cylindrical bore of the chuck sleeve 1C. When the clamp sleeve 5 is rotated clockwise, each needle roller 4 in contact with the tapered inner surface of the clamp sleeve 5 revolves spirally along the outer surface of the chuck sleeve 1C while rotating about its own axis. Thus, the roller-retaining sleeve 2 moves toward the flange 1B, while rotating, in accordance with the revolution of the needle rollers 4, and at the same time the clamp sleeve 5 also moves toward the flange 1B. The movements of the roller-retaining sleeve 2 and the clamp sleeve 5 toward the flange 1B reduce the clearance between the tapered inner surface of the clamp sleeve 5 and the tapered outer surface of the chuck sleeve 1C, so that the clamp sleeve 5 strongly presses the chuck sleeve 1C from the entire outer circumference thereof via the needle rollers 4 in order to reduce the diameter of the chuck sleeve 1C. As a result, the shank 7A of the tool 7 inserted into the cylindrical bore of the chuck sleeve 1C is clamped and held by the chuck sleeve 1C via the spring collet 8. When the clamp sleeve 5 in a clamped state is rotated counterclockwise, the roller-retaining sleeve 2 moves toward the tip end of the chuck sleeve 1C, and the clamp sleeve 5 also moves in the same direction. Therefore, the diameter of the chuck sleeve 1C is restored to its original size, so that the clamping force applied to the tool 7 is released. This enables the tool 7 to be removed from the chuck sleeve 1C or to be replaced with a different tool.
In such a conventional chuck, the chuck sleeve 1C extends from the end surface of the flange 1B opposite the tapered shank portion 1A. Therefore, within an area of the tapered surface 1Ca adjacent to the base portion of the chuck sleeve 1C continuous with the flange 1B, the rigidity against elastic deformation in the radial direction is considerably higher than that in the remaining area. Therefore, when the clamp sleeve 5 is rotated in the clamping direction so as to reduce the diameter of the chuck sleeve 1C, within the above-described area of the tapered surface 1Ca the ratio of reduction in diameter is very small as compared to that in the remaining area.
In order to solve the above-described drawback, one of the present inventors has proposed an improved chuck as shown in U.S. Pat. No. 6,105,974. In the improved chuck, a groove having a predetermined depth is formed in the end surface of the flange opposite the shank portion such that the groove extends along the outer circumference of the bottom end of the chuck sleeve through which the chuck sleeve is joined with the flange. Since the groove increases the effective chucking length of the chuck sleeve; i.e., the length of a portion of the chuck sleeve in which the chuck sleeve can elastically deform in a diameter-reducing direction, elastic deformation of the chuck sleeve in the diameter-reducing direction easily occurs over substantially the entire length of the chuck sleeve. Therefore, the effective chucking length of the chuck sleeve can be increased with no accompanying increase in the overall length of the chuck sleeve.
In the conventional chuck, the change ratio of the inner diameter of the chuck sleeve can be increased to some extent when the clamp sleeve 5 disposed to surround the outer circumferential surface of the chuck sleeve 1C is tightened to a degree such that the end surface of the clamp sleeve 5 abuts the end surface of the flange 1B opposite the tapered shank portion 1A. However, if the tightening operation is continued even after the end surface of the clamp sleeve 5 has abutted the end surface of the flange 1B opposite the tapered shank portion 1A, the tightening force becomes excessive, whereby the chuck sleeve 1C deforms because of a torsion phenomenon. This causes a problem in that the torsional deformation of the chuck sleeve 1C causes deflective vibration in the tool holder 1 and a cutting tool fitted into the chuck sleeve when the tool holder 1 is rotated, making accurate cutting operation impossible.